FIG. 1 of that patent illustrates an aerobic sewage treatment system as used in residential and small commercial installations. The treatment tank is divided into a pretreatment sludge chamber into which sewage discharged from the plumbing system is supplied through an inlet line, an aeration chamber in which the sewage is mixed or stirred and wherein air is mixed into the sewage during this process, and a settling chamber which communicates with the aeration chamber, receives the treated sewage from it, and from which the treated sewage flows into the discharge pipe, thence into a leach bed.
The submerged motor, propeller type of aerator described in said patent produced an upward flow from near the bottom of the aerating chamber, through a tubular housing surrounding the motor, and against a deflector which diverted the flow substantially around 360.degree. of the housing toward all walls of the chamber. This however does not necessarily produce the best over-all agitation and mixing within the chamber because the power requirements placed on the motor are relatively high, yet the flow is diverted so widely that it quickly reduces in velocity and does not stir the liquid in farther regions of the chamber from the housing.
Furthermore, it has been noted that, depending on the load upon the entire system, small particulate matter may rise to the top of the settling chamber and flow outward in the discharge, whereas it is desirable that a minimum of particulate matter leave the tank in the final outflow Therefore, it is desirable to induce a certain amount of recirculation flow from the settling chamber into the aerating chamber, to maximize the dissolution of particles into the liquor before discharge from the system.